1. Field of the Invention
This invention relates to an automotive shock absorber having a unitary striker plate and closure cap which is formed from the outer cylinder of the shock absorber and to a method of manufacturing same.
2. Disclosure Information
Various means and methods have been used for closing the outer cylinders of automotive shock absorbers in the area of the rod guide, which guide permits the shock absorber's piston rod to be coaxially supported and slidingly received within the main body of the shock absorber.
British patent application No. 2,099,956 and U.S. Pat. No. 4,335,871 disclose shock absorbers including an outer cylinder which is rolled over or spun down upon the shock absorber's rod guide. This method of closing a shock absorber presents certain drawbacks for mass production systems intended to produce shock absorber units suitable for use in MacPherson struts. First, because MacPherson struts are subjected to severe rebound shock loading when the strut is fully extended, the material of the outer cylinder and the single thickness spun over section must have sufficient strength to prevent the rod guide from becoming disengaged with the outer cylinder. However, spinning a heavy section having sufficient thickness to withstand the force upon full extension of the shock absorber will not be practicable because heat generated during the spinning process would damage the seals located in the rod guide; alternatively, the rod guide would need to be cooled during the spinning process and this would add undesirable complexity to the production process. Secondly, the inner radius of the bend in a spinning process must be roughly equal to the thickness of the metal being spun and radii of the magnitude which would result from spinning a heavy gauge cylinder would cause problems with gas seals, which would not have a square corner to seat onto. Another problem with spun-over closure systems is that no striker is provided for a jounce bumped mounted upon the piston rod. If such a striker is required, an additional striker plate must be welded onto the closed cylinder and such welding of an additional part may further damage the rod seal while at the same time engendering additional cost and production time.
Although it would be possible to form a closure having a configuration similar to those disclosed in British patent application No. 2,099,956 or U.S. Pat. No. 4,335,871, from a single stroke pressing operation, material of an outer cylinder having sufficient thickness to withstand the axial stresses encountered in such a pressing operation without failing through a buckling mechanism would be so heavy as to produce an uneconomical part in terms of cost and weight.
U.S. Pat. No. 4,480,730 discloses a shock absorber having a closure cap which is crimped to the outer cylinder. This of course necessitates the additional parts comprising the closure cap, which must be installed by means of a unique operation. This system is therefore not subject to the most favorable economics for mass production.
U.S. Pat. No. 4,003,454 discloses an automotive impact shock absorber for use with a bumper system of a motor vehicle in which an interior rod guide is welded to a supporting cylinder.
U.S. Pat. No. 1,656,222 and 3,314,276 disclose in the first case a flared supply pipe and in the second case a bellows formed from a pipe or tube section. In each case, the flared or bellows section extends externally from the cylinder from which it is formed. No internally extending section is disclosed.
It is an object of the present invention to provide an automotive shock absorber having a closure means which is economical in terms of material usage and production time.
It is a further object of the present invention to provide a shock absorber having a closure system which is economical because the shock absorber is closed by a closure cap and striker plate which is unitary with and formed from the outer cylinder of the shock absorber.
It is yet a further object of the present invention to provide an automotive shock absorber having an integral striker plate which may be formed and installed without damaging the piston rod guide seals of the shock absorber.
It is yet a further object of the present invention to provide a method for forming an integral closure cap and striker plate from the outer cylinder of an automotive shock absorber using multiple steps which result in a striker plate having sufficient strength for use with a MacPherson strut formed using an outer cylinder with a wall thickness which could not withstand in a single step the axial compression required to close the cylinder by means of a pressing operation.
It is yet a further object of the present invention to provide a method for assembling automotive shock absorbers without harmful welding processes.
It is yet a further object of the present invention to provide a method for assembling automotive shock absorbers which provides precise control of the length of the shock absorber's outer cylinder and striker plate.